Stabilizing oxygen redox reaction in phase-transition-free P2-type Co/Nifree cathode via Cu doping for sodium-ion batteries  

通过掺杂铜稳定钠离子电池中无相变P2-型无Co/Ni正极中的氧氧化还原反应

作　　者：Hai-Xia Zhang Lin-Rong Wu Hao-Rui Wang Dong-Zheng Wu Shao-Hui Guo Ding Zhang Xiao-Chuan Duan Xian-Ming Zhang 张海霞;吴林蓉;王皓睿;武东政;郭绍晖;张鼎;段小川;张献明(College of Chemical Engineering and Technology,Taiyuan University of Technology,Taiyuan 030024,China;School of Chemical Engineering and Pharmacy,Wuhan Institute of Technology,Wuhan 430205,China)

机构地区：[1]College of Chemical Engineering and Technology,Taiyuan University of Technology,Taiyuan 030024,China [2]School of Chemical Engineering and Pharmacy,Wuhan Institute of Technology,Wuhan 430205,China

出　　处：《Science China Materials》2024年第11期3629-3636,共8页中国科学（材料科学）（英文版）

基　　金：financially supported by the National Natural Science Foundation of China(22271211);the Natural Science Foundation of Shanxi Province(20210302123107 and 202202060301018)。

摘　　要：Due to their high capacity,the P2-type layered oxide cathodes containing oxygen redox reaction processes have attracted wide attention for sodium-ion batteries.However,these materials usually exhibit poor electro-chemical properties,resulting from irreversible oxygen redox reactions and phase transition processes at high voltages,and thus hinder their large-scale application.This work reveals the mechanism for the significantly improved cycle stability and rate performance of Co/Ni-free Na_(0.7)5Li_(0.25-2/3x)CuxMn_(0.75-1/3x)O_(2)via Cu doping.Ex-situ XPS demonstrates that Cu doping reduces the amount of Mn^(3+)that triggers the Jahn-Teller effect during the cycling.In addition,the electron enrichment of oxygen around Cu can alleviate the irreversible oxidation of oxygen,and thus suppressing the phase transition originates from the rapid weakening of the electrostatic repulsion between O-O.Meanwhile,in-situ XRD results verify that the Na_(0.7)5Li_(0.19)Cu_(0.09)Mn_(0.7)2O_(2)maintains the P2 phase structure during charging and discharging,resulting in a near-zero strain characteristic of 1.9%.Therefore,the optimized cathode delivers a high reversible capacity of 194.9 mAh g−1 at 0.1 C and excellent capacity retention of 88.6%after 100 cycles at 5 C.The full cell paired with commercial hard carbon anode delivers energy density of 240 Wh kg−1.Our research provides an idea for designing a new type of intercalated cathode for sodium-ion batteries with low cost and high energy density.含氧氧化还原反应过程的P2-型层状氧化物正极由于具有高容量在钠离子电池中受到广泛关注.然而,由于这些材料在高电压下发生不可逆的氧氧化还原反应和相变过程,通常电化学性能较差,因而阻碍了它们的大规模应用.本研究揭示了通过掺杂铜使无Co/Ni的Na_(0.75-)Li_(0.25-2/3x)Cu_xMn_(0.75-1/3x)O_(2)循环稳定性和速率性能显著提高的机理.非原位XPS显示,掺入Cu可减少循环过程中引发Jahn-Teller效应的Mn^(3+)的量.此外,Cu周围氧的电子富集可以减轻氧的不可逆氧化,从而抑制因O-O之间静电排斥的快速减弱而产生的相变.同时,原位XRD结果证实,Na_(0.75)Li_(0.19)CCu_(0.09)Mn_(0.72)O_(2)在充放电过程中保持了P2相结构,从而实现了1.9%的近零应变特性.因此,优化后的正极在0.1 C时的可逆容量高达194.9 mAh g^(-1),在5 C时循环100次后的容量保持率高达88.6%.与商用硬碳负极配对的全电池可提供240 Wh kg^(-1)的能量密度.我们的研究为设计低成本、高能量密度的新型钠离子电池插层正极材料提供了思路.

关 键 词：sodium-ion batteries Co/Ni-free Cu doping oxygen redox reaction phase transition. 

分 类 号：TM912[电气工程—电力电子与电力传动] O646[理学—物理化学]